1. Field
The present disclosure relates to an electro-acoustic transducer, and more particularly, to a micro-machined electro-acoustic transducer.
2. Description of the Related Art
An electro-acoustic transducer is a device that converts electric energy into acoustic energy or vice versa, and may include an ultrasonic transducer, a microphone, and the like. A micro-machined electro-acoustic transducer includes a micro-electro-mechanical system (MEMS), and a typical example thereof is a micro-machined ultrasonic transducer (MUT). The MUT is a device that converts electric signals into ultrasonic signals or vice versa, and may be classified into a piezoelectric MUT (pMUT), a capacitive MUT (cMUT), a magnetic MUT (mMUT), and the like, according to a converting method of the MUT. Generally, the pMUT has been mainly used, but recently, as the cMUT has been developed, cMUT applications have increased. The cMUT is advantageous in terms of the transmission and reception of broadband signals, integrated manufacturing by using semiconductor processing, and integration with electric circuits. The cMUT is preferred to manufacture medical diagnostic imaging devices and sensors.
Recently, ultrasound devices having broadband characteristics have been actively developed due to an increased demand for various methods of obtaining ultrasound images, such as B-mode imaging, Doppler imaging, harmonic imaging, photoacoustic imaging, and the like. Such ultrasound devices are also necessary for diagnosing organs having different sizes and depth, such as the abdomen, heart, and thyroid. Although the cMUT may transmit and receive signals of a broader frequency band than a general pMUT, the cMUT may not be capable of receiving signals in the entire frequency band. Therefore, methods of combining cells with different resonant frequencies to manufacture electro-acoustic transducers with broadband characteristics are under development.